In Drosophila, as in vertebrates and caenorhabditis elegans, a large family of odorant receptor genes is responsible for the remarkable discriminatory power of the olfactory system. For this capability, it is essential that the brain discern which of the numerous receptors has been activated by an odorant. Several lines of evidence suggest that odorant receptors themselves may provide a link between the odorant recognition properties of a neuron and its central pattern of connectivity, which may specify perception and behavioral response to a particular odor. While recent results of experiments in the mouse do validate a role for odorant receptors in olfactory system development, the mechanisms by which odorant receptors dictate neuronal connectivity are not understood. The experiments proposed here aim to address this problem using Drosophila as the model system. The experimental approach will be to first characterize the developmental expression of odorant receptors and next to examine the consequences of varying the levels of receptor proteins on development of the olfactory nervous system. These studies will contribute towards the understanding of basic principles of neurobiology.